Volume 95, Issue 11, 01 June 2004
Index of content:
- DEVICE PHYSICS (PACS 85)
Variable temperature film and contact resistance measurements on operating n-channel organic thin film transistors95(2004); http://dx.doi.org/10.1063/1.1710729View Description Hide Description
We report structural and electrical properties in thin films of an n-channel organic semiconductor, tetracarboxylic dimide The structure of polycrystallinethin films of was studied using x-ray diffraction and atomic force microscopy. Films order with single crystal-like packing, and the direction of π-π overlap is in the substrate plane. Organic thin film transistors (OTFTs) based on were fabricated on hydrophobic and hydrophilic substrates. OTFTs showed effective mobility as high as 0.1 cm2/V s. Contact resistance of operating OTFTs was studied using resistance versus length plots and a four-probe method for three different contact metals(Au, Ag, Ca). Typical OTFTs had a specific contact resistance of at high gate voltage. There was no dependence of contact resistance with contact metal. Variable temperature measurements revealed that filmresistance in the OTFT was activated in the temperature range 100–300 K, with typical activation energies of 60–80 meV. Contact resistance showed similar activated behavior, implying that the Schottky barrier at the contact is not the limiting resistance for the contact. Filmresistance data showed a Meyer–Neldel relationship with characteristic energy for various samples. The common TFT instability of threshold voltage shift (TVS) was observed in OTFTs. A model is proposed to explain positive TVS in gate bias stress and oxygen exposure experiments. The model is based on the formation of a metastable complex between and oxygen, which creates a deep acceptor-like trap state.
95(2004); http://dx.doi.org/10.1063/1.1710719View Description Hide Description
The effect of 2 MeV proton irradiation on the current–voltage characteristics of resonant interband tunnelingdiodes (RITDs) is reported. A fluence of causes the peak current to increase by about 4% the valley current to nearly double and the peak-to-valley current ratio to be reduced by about half. At comparable fluences, most minority carrier diodes are inoperational. Radiation-induced changes are compared to changes in the curves of irradiated Si- and GeEsaki diodes, GaSb-based RITDs and InP-based resonant tunneling diodes.
Simulation of hot electron and quantum effects in AlGaN/GaN heterostructure field effect transistors95(2004); http://dx.doi.org/10.1063/1.1719262View Description Hide Description
We report on simulations of electrical characteristics of AlGaN/(InGaN)/GaN heterostructurefield effect transistors with quantum and hot electroneffects taken into account. Polarization charges lead to quantum confinement of electrons in the channel and to the formation of two-dimensional electron gas. The electron quantization leads to the spread of the electronwave function into the barrier and bulk but does not have significant impact on dc electrical characteristics.Hot electrons play an important part in the charge transport by spilling over into the bulk GaN where they are captured by traps. This leads to negative differential conductivity, which is also observed experimentally. The simulation results are in good agreement with measured dccharacteristics.
95(2004); http://dx.doi.org/10.1063/1.1719264View Description Hide Description
Defect-related localized electronic states in AlGaN/GaN transistors give rise to commonly observed charge trapping phenomena. Electron dynamics through the trapping centers is strongly affected by electric fields, which can exceed values of during device operation. The field-assisted emission characteristics provide a unique way to determine the physical properties of the trapping centers. We present a detailed study of the effects of electric field and temperature on the rate of electron emission from the barrier traps in AlGaN/GaN high-electron-mobility transistors. We demonstrate that for temperatures above 250 K, the Poole-Frenkel (PF) emission is the dominant mechanism for electrons to escape from the trapping centers. The emission rate increases exponentially with the square root of the applied field consistent with the decrease of the apparent activation energy predicted by the PF model. We find that the observed trapping center is described by the attractive long-range Coulomb potential with the zero-field binding energy of ∼0.5 eV.